Effect of operating voltage on microstructure and microhardness of NiCoCrAlYTa-Y2O3 composite coatings on single crystal superalloy produced by electrospark deposition

Abstract

NiCoCrAlYTa-Y2O3 metal matrix composite coatings were prepared on single crystal superalloy by electrospark deposition (ESD) to improve the wear- and oxidation resistance. The effect of operating voltage during ESD on the deposit morphology, coating growth kinetics, microstructure and properties was investigated. The results showed that, with increasing operating voltage, the dimension (both diameter and depth) of single-pulse deposit increased, leading to thinner deposit thickness, thus resulting in higher cooling rate, finer grains, stronger crystal orientation, and increasing microhardness. Whereas the motion of the molten deposit metal became more turbulent, giving rise to the defect of lack of fusion. However, the grain size increased obviously from bottom layer to top layer for 100 V condition, leading to decreasing microhardness. Meanwhile, the mass gain rate increased but the mass transfer coefficient decreased with the increase of operating voltage. The distribution pattern of Y2O3 particles changed during electrospark deposition, from gathering in the boundary between the powders in the electrode to distributing homogeneously in the whole coating, which contributed to the increase of coating microhardness.